CVE-2024-56681

What it actually does

The ahash_hmac_init function in the Linux kernel crypto bcm driver fails to check the return value of ahash_init, allowing it to return success even when ahash_init encounters an error such as -ENOMEM during memory allocation.

Why it matters to the business

Organizations running affected Linux kernels may experience unreliable cryptographic operations in the kernel, leading to potential system instability, failed security functions, or degraded performance under memory pressure; urgency is low given the age since publication and absence from known exploitation lists.

How an attack unfolds

An attacker with the ability to influence kernel crypto operations could trigger memory allocation failures during ahash_init calls; because the error is not propagated, the system proceeds in an inconsistent state that could be leveraged in combination with other kernel issues by espionage or financially motivated actors targeting Linux environments.

How to fix it

Update the Linux kernel to the fixed commit 8f1a9a960b1107bd0e0ec3736055f5ed0e717edf or apply the equivalent stable patch; for listed xerces-c packages on Ubuntu releases, upgrade to the specified fixed versions such as 3.1.3+debian-1ubuntu0.1~esm1 for 16.04 LTS.

How to confirm the fix worked

Confirm the running kernel includes the error check in ahash_hmac_init; review git history for the referenced commit and verify package versions match the fixed releases for affected distributions.

Typical attack path

1. Identify a system using the vulnerable bcm crypto ahash implementation
2. Induce memory pressure or allocation failure conditions during hmac initialization
3. Trigger ahash_hmac_init without proper error handling
4. Exploit resulting inconsistent kernel state in conjunction with other vulnerabilities

How to detect it

Search kernel logs and audit trails for unexpected -ENOMEM returns from ahash_init during hmac operations; correlate with crypto subsystem activity and monitor for any unhandled error paths in bcm driver code.

What your security team should do

• Prioritize kernel updates on all systems using the bcm crypto driver
• Monitor EPSS trends and threat actor reports for any increase in exploitation activity
• Test patches in non-production environments before broad deployment
• Review dependent packages and downstream ecosystem impact given prevalence data